SF: Move DispSync systrace logging to shell variable.

screenshot: https://screenshot.googleplex.com/Jo0r6yus6HL

Test: SF tests pass.

Change-Id: I0703507b32648a7afc840811cebf994cc528d9a5
diff --git a/services/surfaceflinger/Scheduler/DispSync.h b/services/surfaceflinger/Scheduler/DispSync.h
index 89f5cdb..5b511f4 100644
--- a/services/surfaceflinger/Scheduler/DispSync.h
+++ b/services/surfaceflinger/Scheduler/DispSync.h
@@ -241,6 +241,9 @@
     bool mIgnorePresentFences;
 
     std::unique_ptr<Callback> mZeroPhaseTracer;
+
+    // Flag to turn on logging in systrace.
+    bool mTraceDetailedInfo = false;
 };
 
 } // namespace impl